As electronic devices increasingly become portable, advances must be made in energy storage devices to enable such portability. Indeed, it is often the case with current electronics technology that the limiting factor to portability of a given device is the size and the weight of the associated energy storage device. Obviously, a small energy storage device may be fabricated for a given electrical device application, but at the cost of energy capacity. Conversely, a large energy storage device yielding long life may be attached to an electronic device, but typically at the expense of size and portability. The result is that either the energy storage device is too bulky, too heavy, or does not last long enough for a given application. Typical energy storage devices used for portable electronics include the electrochemical battery cell, and, increasingly, the electrochemical capacitor.
Electrochemical capacitors are a class of devices characterized by relatively high power densities as compared with conventional battery systems. The charge mechanism of such capacitors is typically the result of primary, secondary, tertiary, and higher order oxidation/reduction reactions between the electrodes and the electrolyte of the capacitor.
Currently, there are few commercially available devices which can provide the high current pulses and high power density required for pulse communications, load leveling, and portable power tools, as well as electrochemical capacitors. This is due to the fact that such applications typically require high currents of several to 50 amperes for short time durations, i.e., on the order of 0.10 to 100 milliseconds. These device applications also require long cycle life, for example on the order of between 10.sup.5 and 10.sup.8 cycles and a wide temperature range during operation, i.e., on the order of -30.degree. to 60.degree. C. Traditional battery cells do not have such long usable lives, particularly when subjected to pulse discharge conditions as are commonly experienced in the device applications described above. Conventional electrolytic capacitors have been explored for such applications, but are generally too large to meet the capacitance requirements.
Numerous new materials have been proposed for use in electrochemical charge storage capacitor devices. For example, a novel nickel-chromium-molybdenum based material is disclosed and claimed in previously mentioned U.S. Pat. No. 5,429,895. Such materials may be advantageously paired with appropriate counter electrodes such as, for example, with a zinc electrode, and an appropriate electrolyte disposed therebetween such as, for example, a polymeric matrix having dispersed therein a liquid or solid electrolyte active species, such as KOH.
Heretofore, in such devices, the nickel-chromium-molybdenum alloy electrode was activated by the KOH in the electrolyte after the cell had been assembled. However, as devices become increasingly large to handle larger power and energy density requirements, not all of the electrode material can be sufficiently activated, i.e., the surface of the electrode material was not sufficiently oxidized to generate a layer which would serve as the site for the primary, secondary, tertiary and higher order oxidation/reduction reactions which characterize the device performance. This is mainly due to the fact that there is insufficient KOH in the electrolyte, and hence insufficient OH.sup.- ions for both the development of the active oxide layer, and the oxidation/reduction reactions which occur during cycling.
Accordingly, there exists a need for a method of pretreating electrodes for high power density charge storage devices, to provide a sufficient surface oxide layer on the electrode surface. The pre-activation process should be relatively simple, inexpensive, and yield highly reliable, accurate results. Moreover, the process should not complicate the manufacturing process.